Adénylate cyclase
Activation: The adénylate cyclase is activated by varied ways of indication (receiving coupled with the Protéines G)
Effect: it allows the synthesis of AMPc, (cyclized derivative of ATP)
Consequences: AMPc is able to activate other proteins (Kinases, activation of phosphorylation cascades), and to continue the transduction of the signal of outside towards the interior of the cell. AMPc is then called second messenger.
Mechanism of activation
At rest the Kinase protein has (AMPc dependant or PKA) consists of 4 sub-units: 2 regulating sub-units (R2) and 2 catalytic sub-units (C2). There exists a very strong affinity of R2 for C2. During the fixing of a hormone on the receiver there is formation of a Hormone complex - Receiver which will activate a protein of the type Gs (stimulative) or Gi (inhibiting). This protein activates in its turn Adénylate Cyclase which transforms the ATP into AMPc (second messenger). When 4 molecules of AMPc are fixed on the regulating sub-units of the PKA, there is dissociation of the complex R2 - C2 by reduction in the affinity of R2 for C2. The catalytic sub-units thus released have two evolutions:
- an effect cytosolic or membrane: phosphorylation of ionic, receiving channels membrane or proteins cytoplasmic.
- a nuclear effect: the catalytic sub-units penetrate in the core and act on proteinic complexes: CREB (camp response element-binding). The sub-units will transform CREB into CREB - Phosphate, this phosphorylation allows the activation or the repression of a gene.
Mechanism of inactivation
The return at rest is carried out by the degradation of AMPc in 5' AMP thanks to an enzymatic complex: the phosphodiestérase (PDE).
See too
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